Airfoil design is a critical component to achieving optimal performance in both fixed airfoils such as wings, tails and vertical stabilizers, and rotary airfoils such as propeller blades. The upstream or leading edge designs of prior art airfoils are generally smooth, convex, aerodynamic shapes regardless of the speed of the airflow encountered by the airfoil. However, subsonic airflow and supersonic airflow have different behavior characteristics when obstructions are encountered. Leading edge designs that permit efficient performance in one type of airflow may not be as efficient in the other type of airflow. For example, airfoils which are designed for supersonic airflow perform less efficiently in subsonic airflow due to the very sharp cross-sectional shape at the leading edge. Moreover, supersonic airfoils require expensive heat-resistant materials to avoid thermal damage to the airfoil due to the very high temperatures developed by shock waves in supersonic airflow. Supersonic jet aircraft need a leading edge design that is capable of being optimal for each type of airflow.